Modeling lateral carbon fluxes for agroecosystems in the Mid-Atlantic region: Control factors and importance for carbon budget

Authors: LUO, X - University Of Maryland; RISAL, A - University Of Maryland; QI, J - University Of Maryland; LEE, S - University Of Seoul; Zhang, Xuesong; Alfieri, Joseph; McCarty, Gregory

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2023
Publication Date: 12/7/2023
Citation: Luo, X., Risal, A., Qi, J., Lee, S., Zhang, X., Alfieri, J.G., McCarty, G.W. 2023. Modeling lateral carbon fluxes for agroecosystems in the Mid-Atlantic region: Control factors and importance for carbon budget. Science of the Total Environment. 912:169128. https://doi.org/10.1016/j.scitotenv.2023.169128.
DOI: https://doi.org/10.1016/j.scitotenv.2023.169128

Interpretive Summary: Managing agroecosystems to mitigate greenhouse gas (GHG) emissions is essential for achieving the global goal of reducing climate change risks. The current carbon accounting approaches often include soil organic carbon change and net ecosystem exchange between land and the atmosphere, but do not consider the lateral carbon fluxes that leave the agricultural field and enter the aquatic ecosystems. Here, we employ the Soil and Water Assessment Model -Carbon (SWAT-C) model to demonstrate the significance of lateral carbon fluxes to the assessment of carbon balance of agroecosystems in the Tuckahoe Creek Watershed (TCW) in eastern Maryland, US. We found that lateral carbon fluxes account for approximately 11% of Net Ecosystem Exchange and 95% of net biome production. Overall, the results illustrate the importance of accounting both vertical and lateral carbon fluxes for designing effective agricultural practices to reduce GHG emissions.

Technical Abstract: Estimating lateral carbon fluxes in agroecosystems presents challenges due to intricate anthropogenic and biophysical interactions. In this study, we used a modeling technique to enhance our comprehension of the determinants influencing lateral carbon fluxes and their significance in comparison to vertical carbon fluxes. We refined the SWAT-C model by incorporating a dynamic dissolved inorganic carbon (DIC) module, enhancing our ability to accurately quantify total lateral carbon fluxes. This improved model was then calibrated using observed data on riverine particulate organic carbon (POC) and dissolved organic carbon (DOC) fluxes, as well as net ecosystem exchange (NEE) data monitored by a flux tower situated in a representative agricultural watershed, the Tuckahoe Watershed (TW) of the Chesapeake Bay's coastal plain. We assessed the losses of POC, DOC, and DIC across five primary rotation types: C (continuous carbon), CS (corn-soybean), CSS (corn-soybean-soybean), CWS (corn-wheat-soybean), and CWSCS (corn-wheat-soybean-corn-soybean). Subsequently, we delved into the determining factors influencing annual POC, DOC, and DIC loads in the TW's agroecosystem, considering climate, topography, soil properties, hydrology, and soil organic carbon budget components. Lastly, we explored the correlation between vertical carbon fluxes [net ecosystem production (NEP), NEE, and net biome production (NBP)] and lateral ones [total lateral carbon fluxes (POC+DOC+DIC) and grain yield carbon]. Our study revealed notable variations in the average annual fluxes of POC (ranging between 152-198 kg/ha), DOC (74-85 kg/ha), and DIC (93-156 kg/ha) across the five rotation types, underscoring the impact of rotational practices on POC, DOC, and DIC dynamics within the TW’s agroecosystem. The primary influencing factor for annual POC fluxes was identified as sediment yield. While both annual DOC and DIC fluxes displayed a marked correlation with surface runoff across all crop rotation schemes, soil respiration also significantly influenced annual DIC fluxes. Total lateral carbon fluxes constituted roughly 11% of both NEP and NEE, yet they represented a striking 95% of NBP in the TW’s agroecosystem. Grain yield carbon accounted for 80% of both NEP and NEE and was nearly seven times that of NBP. Our findings suggest that introducing soybeans into corn fields tends to reduce NEP, NEE, and also NBP. With a rotation pattern of two successive soybean crops followed by corn, NBP turned negative, hinting at a net carbon source. Conversely, integrating winter wheat into the corn-soybean rotation significantly boosted NEP, NEE, and NBP values, with NBP even surpassing the levels in continuous corn cultivation.